The present invention relates to drop-on-demand printheads of the type which selectively print drops of ink in a print line on a web or sheet which moves relatively to the printhead.
Drop-on-demand printheads have been used to form travelling printheads for printing the height of one or a few print lines at a time. Certain developments in drop-on-demand printhead design give the prospect of low cost nozzle module assemblies which can be mounted fixed in the printer to form a wide printbar substantially spanning the width of the paper. Recent advances in printhead reliability make this prospect practical as well as economical. Specifically, the above noted related applications describe such drop-on-demand printhead design developments. OBJECTS OF THE INVENTION
It is a basic object of the present invention to provide an improved drop-on-demand printhead for selectively printing drops of ink in a print line on a web or sheet which is movable in relation to the printhead.
It is a further object of the invention to provide a drop-on-demand printhead which is mounted fixed in a printer to form a wide printbar substantially spanning the width of the print surface.
It is another object of the invention to provide a drop-on-demand printhead of the foregoing type which is both economical to manufacture and reliable in operation.
In accordance with these and other objects, a drop-on-demand printhead constructed according to the invention comprises a plurality of vertically oriented stacks of print modules arranged in abutting relation to form a plurality of laterally offset layers of print modules. Each module in each of the layers provides at least one group of lateral uniformly spaced ink ejectors. Successive groups of ejectors in each layer are laterally spaced by the same amount such that drops from vertically overlapping portions of ejector groups from different module layers interleave to form a segment of a print line. The density of the segment is equal to the product of the drop deposition density of each group and the number of groups contributing to form the segment. Preferably, the number of ejector groups combining to form the print line segment is one less than the number of layers. Ink supplies and housekeeping fluids are preferably distributed through each stack individually. Make-up ink supplies are coupled to the modules through a riser extending through each respective stack. Each stack also includes an air duct arrangement forming a continuous air supply passage through the module layers.
According to a further aspect of the invention, a housekeeping manifold is provided for each module which communicates with the air duct arrangement to supply environment fluids to or exhaust such fluids from the vicinity of the ink ejecting apertures of each module.